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Very fine crystalline or glassy rock of volcanic origin, composed chiefly of sodic plagioclase and free silica with subordinate dark-colored minerals.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



a magmatic rock that is the effusive equivalent of granodiorite and quartz-diorite. Dacite consists of a finegrained or vitreous basic mass and phenocrysts of plagioclase and quartz, more rarely, of hornblende, biotite, and pyroxene, and sometimes, sanidine. Where albitization processes are widely developed, dacite turns into quartz al-bitophyre. Dacites were ejected by volcanoes in the Paleozoic (in the Urals, for example), Mesozoic, and Cenozoic (in the Caucasus, for example). They are also found among modern lavas on Kamchatka.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
The population distributions of the Zanbil adakitic dacites were modeled by mixing together two populations of crystals with linear CSDs, termed fine grains and phenocrysts, for both amphibole and plagioclase.
Porphyritic andesite to dacite lava flows (Lava Dacttica Apilulco; thickness < 4 m) with planar fracturing subparallel to the surface constitute the main effusive products.
Trachytes have more K-feldspar than plagioclase and biotite and no quartz compared to dacites. Plagioclase phenocrysts show oscillatory to patchy zoning.
Firstly, the rocks of the NW part of the Iberian Chain have more evolved compositions (basalts to dacites), higher degrees of alteration (Table 2) and no peridotite xenoliths.
The Pliocene volcanics are generally dominated by andesites, whereas dacites occur as dominant phase in Pleistocene volcanics.
Verma (1999) reported that andesites and dacites from the Sierra de Chichinautzin volcanic field (central MVB) were derived from partial melting of a heterogeneous mafic granulite from the lower crust.
The geologic history of this deposit[4] begins with the intrusion of stocks of tonalitic composition (the Andacollo porphyry, Upper Cretacous) within a layered sequence of andesite and dacites, which induced pervasive hydrothermal alteration (K silicate, quartz sericite) and mineralization (mainly pyrite-chalcopyrite plus some minor quantities of molybdenite, bornite, cubanite and pyrrhotite).
The metaconglomerate is poorly deformed and contains cm-size pebbles of sandstones, pelites, cherts, limestones, plutonic rocks (quartz-diorites, tonalites and granitoids) and volcanic rocks (basalts, andesites, dacites and glass fragments).